Project Summary: Posttraumatic stress disorder (PTSD), a serious public health epidemic, affects approximately 20% of the 18.5 million U.S. veterans, and places them at higher risk for impaired biopsychosocial functioning. Individuals with PTSD experience comorbidities including: major depression, mania, panic attacks, social phobia, and alcohol/drug dependence. Similarly they have increased odds of symptoms and diseases including: low psychological well- being, days of disability, chronic lung disease, arthritis, migraines, hypertension, heart disease, ulcers, cancer, chronic fatigue syndrome, and multiple chemical sensitivities. Increases in PTSD symptom severity (PTSDSS) cause an inability to regulate emotions, control impulsive behaviors, and function within family and society oftentimes leading to homelessness, divorce, and spousal/child abuse. Unfortunately, suicide rates are surging with about 7,300 veterans taking their life each year, more than die in combat. Alarming veteran PTSD rates and the insidious effects of this condition demand empirically validated treatment programs. VA intensive PTSD programs reach only 1% of the veterans and typically led to modest symptom improvement. As a result many veterans self-treat their PTSD with non-pharmacological means; efforts to suppress their emotions can further their symptoms. Anecdotal evidence suggests that training service dogs (SDs) may be rehabilitative for veterans with PTSD, but evidence of efficacy is lacking. We hypothesize that veterans with PTSD who train SDs for fellow veterans will show a reduction in PTSDSS and decreases in stress-related biological and psychosocial outcomes. Despite belief in the value of SDTPs as a treatment option for veterans with PTSD, we are unable to locate any published peer-reviewed studies that evaluate the efficacy of a SDTP in veterans with PTSD. This study addresses gaps in evidence-based alternative interventions for PTSD, a critical need given the meager successes of standard therapies. This randomized clinical trial evaluates the efficacy of an 8-week SDTP compared to a wait list control intervention for improving primary outcome: PTSDSS, secondary outcomes: stress and psychosocial health, and exploratory outcome: cellular aging in veterans with PTSD. We also evaluate the SDs stress during training and feasibility of the intervention for veterans with PTSD. If the SDTP is successful in reducing PTSDSS in veterans with PTSD and without stressing the dogs it may prove to be a cost-effective rehabilitative opportunity for other at-risk populations. This study is novel in evaluating the effects of the SDTP on the human and the dog and is potentially generalizable and scalable with a broad reach for future implementation and dissemination.